]>
Commit | Line | Data |
---|---|---|
e26accaa JR |
1 | .\" Copyright (c) 1986 The Regents of the University of California. |
2 | .\" All rights reserved. | |
3 | .\" | |
4 | .\" Redistribution and use in source and binary forms are permitted | |
5 | .\" provided that the above copyright notice and this paragraph are | |
6 | .\" duplicated in all such forms and that any documentation, | |
7 | .\" advertising materials, and other materials related to such | |
8 | .\" distribution and use acknowledge that the software was developed | |
9 | .\" by the University of California, Berkeley. The name of the | |
10 | .\" University may not be used to endorse or promote products derived | |
11 | .\" from this software without specific prior written permission. | |
12 | .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR | |
13 | .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED | |
14 | .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. | |
15 | .\" | |
16 | .\" @(#)resolver.5 5.9 (Berkeley) 12/14/89 | |
17 | .\" $Id$ | |
18 | .\" | |
19 | .Dd November 11, 1993 | |
20 | .Dt RESOLVER 5 | |
21 | .Os BSD 4 | |
22 | .Sh NAME | |
23 | .Nm resolver | |
24 | .Nd resolver configuration file | |
25 | .Sh SYNOPSIS | |
26 | .Pa /etc/resolv.conf | |
27 | .Sh DESCRIPTION | |
28 | The | |
29 | .Nm resolver | |
30 | is a set of routines in the C library | |
31 | .Pq Xr resolve 3 | |
32 | that provide access to the Internet Domain Name System. | |
33 | The | |
34 | .Nm resolver | |
35 | configuration file contains information that is read | |
36 | by the | |
37 | .Nm resolver | |
38 | routines the first time they are invoked by a process. | |
39 | The file is designed to be human readable and contains a list of | |
40 | keywords with values that provide various types of | |
41 | .Nm resolver | |
42 | information. | |
43 | .Pp | |
44 | On a normally configured system, this file should not be necessary. | |
45 | The only name server to be queried will be on the local machine, | |
46 | the domain name is determined from the host name, | |
47 | and the domain search path is constructed from the domain name. | |
48 | .Pp | |
49 | The different configuration directives are: | |
50 | .Bl -tag -width "nameser" | |
51 | .It Li nameserver | |
52 | Internet address (in dot notation) of a name server that the | |
53 | .Nm resolver | |
54 | should query. Up to | |
55 | .Dv MAXNS | |
56 | (see | |
57 | .Pa <resolv.h> ) | |
58 | name servers may be listed, one per keyword. | |
59 | If there are multiple servers, the | |
60 | .Nm resolver | |
61 | library queries them in the order listed. | |
62 | If no | |
63 | .Li nameserver | |
64 | entries are present, the default is to use the name server on the local machine. | |
65 | (The algorithm used is to try a name server, and if the query times out, | |
66 | try the next, until out of name servers, | |
67 | then repeat trying all the name servers | |
68 | until a maximum number of retries are made). | |
69 | .It Li domain | |
70 | Local domain name. | |
71 | Most queries for names within this domain can use short names | |
72 | relative to the local domain. | |
73 | If no | |
74 | .Li domain | |
75 | entry is present, the domain is determined from the local host name returned by | |
76 | .Xr gethostname 2 ; | |
77 | the domain part is taken to be everything after the first | |
78 | .Sq \&. . | |
79 | Finally, if the host name does not contain a domain part, the root | |
80 | domain is assumed. | |
81 | .It Li search | |
82 | Search list for host-name lookup. | |
83 | The search list is normally determined from the local domain name; | |
84 | by default, it contains only the local domain name. | |
85 | This may be changed by listing the desired domain search path | |
86 | following the | |
87 | .Li search | |
88 | keyword with spaces or tabs separating the names. | |
89 | Most | |
90 | .Nm resolver | |
91 | queries will be attempted using each component | |
92 | of the search path in turn until a match is found. | |
93 | Note that this process may be slow and will generate a lot of network | |
94 | traffic if the servers for the listed domains are not local, | |
95 | and that queries will time out if no server is available | |
96 | for one of the domains. | |
97 | .Pp | |
98 | The search list is currently limited to six domains | |
99 | with a total of 256 characters. | |
100 | .It Li sortlist | |
101 | Allows addresses returned by gethostbyname to be sorted. | |
102 | A | |
103 | .Li sortlist | |
104 | is specified by IP address netmask pairs. The netmask is | |
105 | optional and defaults to the natural netmask of the net. The IP address | |
106 | and optional network pairs are separated by slashes. Up to 10 pairs may | |
107 | be specified. For example: | |
108 | .Bd -literal -offset indent | |
109 | sortlist 130.155.160.0/255.255.240.0 130.155.0.0 | |
110 | .Ed | |
111 | .It Li options | |
112 | Allows certain internal | |
113 | .Nm resolver | |
114 | variables to be modified. | |
115 | The syntax is | |
116 | .D1 Li options Ar option ... | |
117 | where | |
118 | .Ar option | |
119 | is one of the following: | |
120 | .Bl -tag -width "ndots:n " | |
121 | .It Li debug | |
122 | sets | |
123 | .Dv RES_DEBUG | |
124 | in | |
125 | .Ft _res.options . | |
126 | .It Li ndots: Ns Ar n | |
127 | sets a threshold for the number of dots which | |
128 | must appear in a name given to | |
129 | .Fn res_query | |
130 | (see | |
131 | .Xr resolver 3 ) | |
132 | before an | |
133 | .Em initial absolute query | |
134 | will be made. The default for | |
135 | .Ar n | |
136 | is | |
137 | .Dq 1 , | |
138 | meaning that if there are | |
139 | .Em any | |
140 | dots in a name, the name will be tried first as an absolute name before any | |
141 | .Em search list | |
142 | elements are appended to it. | |
143 | .It Li timeout: Ns Ar n | |
144 | sets the amount of time the resolver will wait for a response from a remote | |
145 | name server before retrying the query via a different name server. Measured in | |
146 | seconds, the default is | |
147 | .Dv RES_TIMEOUT | |
148 | (see | |
149 | .Pa <resolv.h> ). | |
150 | .It Li attempts: Ns Ar n | |
151 | sets the number of times the resolver will send a query to its name servers | |
152 | before giving up and returning an error to the calling application. The | |
153 | default is | |
154 | .Dv RES_DFLRETRY | |
155 | (see | |
156 | .Pa <resolv.h> ). | |
157 | .It Li rotate | |
158 | sets | |
159 | .Dv RES_ROTATE | |
160 | in | |
161 | .Ft _res.options , | |
162 | which causes round robin selection of nameservers from among those listed. | |
163 | This has the effect of spreading the query load among all listed servers, | |
164 | rather than having all clients try the first listed server first every time. | |
165 | .It Li no-check-names | |
166 | sets | |
167 | .Dv RES_NOCHECKNAME | |
168 | in | |
169 | .Ft _res.options , | |
170 | which disables the modern BIND checking of incoming host names and mail names | |
171 | for invalid characters such as underscore (_), non-ASCII, or control characters. | |
172 | .It Li inet6 | |
173 | sets | |
174 | .Dv RES_USE_INET6 | |
175 | in | |
176 | .Ft _res.options . | |
177 | This has the effect of trying a AAAA query before an A query inside the | |
178 | .Ft gethostbyname | |
179 | function, and of mapping IPv4 responses in IPv6 ``tunnelled form'' if no | |
180 | AAAA records are found but an A record set exists. | |
181 | .El | |
182 | .El | |
183 | .Pp | |
184 | The | |
185 | .Li domain | |
186 | and | |
187 | .Li search | |
188 | keywords are mutually exclusive. | |
189 | If more than one instance of these keywords is present, | |
190 | the last instance wins. | |
191 | .Pp | |
192 | The | |
193 | .Li search | |
194 | keyword of a system's | |
195 | .Pa resolv.conf | |
196 | file can be | |
197 | overridden on a per-process basis by setting the environment variable | |
198 | .Dq Ev LOCALDOMAIN | |
199 | to a space-separated list of search domains. | |
200 | .Pp | |
201 | The | |
202 | .Li options | |
203 | keyword of a system's | |
204 | .Pa resolv.conf | |
205 | file can be amended on a per-process basis by setting the environment variable | |
206 | .Dq Ev RES_OPTIONS to a space-separated list of | |
207 | .Nm resolver | |
208 | options as explained above under | |
209 | .Li options . | |
210 | .Pp | |
211 | The keyword and value must appear on a single line, and the keyword | |
212 | (e.g., | |
213 | .Li nameserver ) | |
214 | must start the line. The value follows the keyword, separated by white space. | |
215 | .Sh FILES | |
216 | .Pa /etc/resolv.conf | |
217 | .Pa <resolv.h> | |
218 | .Sh SEE ALSO | |
219 | .Xr gethostbyname 3 , | |
220 | .Xr hostname 7 , | |
221 | .Xr named 8 , | |
222 | .Xr resolver 3 , | |
223 | .Xr resolver 5 . | |
224 | .Dq Name Server Operations Guide for Sy BIND |